The use of catalysts formed by supporting Group VIII non-noble metals and Group VI-B metals (Periodic Table of the Elements, E. H. Sargent & Company; Copyright 1962 Dyna-Slide Co.), e.g., Ni/Mo, Co/Mo, Ni/Co/Mo, Ni/W, Co/W, Ni/Co/W and the like upon porous refractory inorganic oxides, particularly alumina, to catalytically remove sulfur from petroleum fractions, crude oils, and other mixtures of hydrocarbons has been known for many years. Sulfur removal is necessary since its presence in appreciable amounts gives rise to serious corrosion and refining problems. In many refinery processes, especially those using catalysts, feed sulfur is very deleterious in that it causes excessive catalyst deactivation and loss of yield of the desired product. Gasoline should be relatively free of sulfur to make it compatible with lead anti-knock compounds, and to improve its color and odor stability. In particular, in reforming (hydroforming) processes used to make high octane gasoline, sulfur compounds, even in the 1-20 parts per million, (wppm) range contribute to loss of catalyst activity and C.sub.5.sup.+ liquid yield. In the last decade, in particular, polymetallic metal catalysts have been employed to provide, at reforming conditions, improved catalyst activity, selectivity and stability. Thus, additional metallic components have been added to the more conventional platinum catalysts as promotors to further improve, particularly, the activity or selectivity, or both, of the basic platinum catalyst, e.g., iridium, rhenium, selenium, tin, and the like. In the use of these catalysts it has become essential to reduce the feed sulfur to only a few wppm. For example, in the use of platinum-rhenium catalysts it is generally necessary to reduce the sulfur concentration of the feed well below about 2 wppm, and preferably well below about 0.1 wppm, to avoid excessive loss of catalyst activity and C.sub.5.sup.+ liquid yield. By removing virtually the last traces of sulfur from the naphtha feed, considerable improvement in activity and C.sub.5.sup.+ liquid yield of high octane product are achieved. Stability advantages also occur enabling longer catalyst life and run length to be realized.
The sulfur-containing feed, prior to reforming, is generally treated over a hydrofining catalyst, e.g., a Co/Mo catalyst, and major amounts of the sulfur are catalytically removed in the form of hydrogen sulfide, H.sub.2 S. However, due to the presence of small amounts of olefins, it is possible for some of the H.sub.2 S to recombine with the olefins upon cooling and to form trace amounts of undersirable sulfur compounds predominantly in the form of mercaptans. This trace residual sulfur can then be removed from the naphtha reformer feed by adsorption over copper chromite or catalysts containing nickel. These metals have been found useful per se, or have been supported on high surface area refractory inorganic oxide materials such as alumina, silica, silica/alumina, clays, kieselguhr, and the like. For example, a massive nickel catalyst containing 50-60% nickel on kieselguhr has been used. Such catalysts become sulfur saturated, and in the present state-of-the-art are not generally regenerated, but discarded or processed for metals recovery.
The earlier mentioned Group VI-B/VIII catalysts have thus conventionally been used to hydroprocess, or hydrodesulfurize, various hydrocarbon fractions to catalytically remove not only sulfur, but also nitrogen, from the hydrocarbon fractions. In hydroprocessing such feeds as vacuum gas oils, atmospheric or vacuum residua, shale, coal liquid fractions and the like, however, not only is sulfur removed from the feed, but also nickel and vanadium. As a result, these metals together with sulfur, carbonaceous material, or coke, and other materials are deposited on the catalysts gradually rendering them inactive. Thus, the catalyst not only contains its original metals, but additionally nickel and vanadium. After extended use, the catalyst becomes sufficiently inactive that it is no longer suitable for use in commercial operation, and hence it must be replaced. It has little value, and in conventional practice it is replaced by a fresh catalyst.